Pact of the Chain Warlocks need to take the Voice of the Chain Master Invocation to be able to communicate with their familiar at those large distances. By default, they're restricted to 100 ft for telepathically communicating with their familiar. The familiar can still travel a farther (unlimited) distance away, but would just need to return to within 100ft of their master in order to communicate/see through eyes/hear through ears.
But yes, it would be a bit much if your familiar could explore all the maps in BG3. In tabletop, a DM can introduce complications to prevent this type of thing, but for a video game with set rules, it makes some sense to prevent solo familiar exploration.
